New Discoveries in Arizona May Be ‘Game-Changers’ in Mystery of Ancient Culture’s Collapse

The remains of houses, bits of charcoal, and rarely seen types of pottery are tantalizing new clues in one of the more persistent mysteries of Southwestern history: What happened to the culture known as the Hohokam?

Best known for their hulking adobe complexes, like the ruins now called Casa Grande, the Hohokam were one of the Southwest’s most complex and influential societies, constructing irrigation canals that turned parts of the Sonoran Desert into farmland, and trading with distant Mesoamerican cultures whose influence can still be seen in Hohokam ball courts.

By the late 1300s, the Hohokam were perhaps the most populous cultural group in the Southwest. But around this time, something triggered their precipitous decline.

While the cause — or, more likely, series of causes — remains poorly understood, Dr. Deni Seymour says she has turned up an important clue: Despite what most scientists have believed for decades, the Hohokam were not alone.

Years of research in southeastern Arizona, the heart of the Hohokam homeland, have turned up what Seymour calls “abundant evidence” that another tribal group — the O’odham, whose members still call Arizona home today — lived in the region perhaps as early as the 1100s.

This flies in the face of scientific convention, which has held that the region was essentially vacant between the fall of the Hohokam in the late 1300s and the arrival of the first Spanish missionaries in the mid-1500s.

“Some of the big questions scholars have been asking for a very long time are: What happened to the Hohokam? Is there a relationship between the Hohokam and the O’odham? In other words, did the Hohokam become the O’odham?” said Seymour, an archaeologist with the Jornada Research Institute in New Mexico, and a specialist in early O’odham and Apache cultures.

“Until now we have not had enough information on the O’odham — historically, the Upper Pima — to address this question from an archaeological standpoint. Now we do.”

In a paper recently published in the Old Pueblo Archaeology Bulletin, Seymour describes her investigations of sites inhabited by a people known as the Sobaípuri, a branch of the O’odham whose descendants are now part of the Tohono O’odham.

Their traces are found mostly along the San Pedro, Santa Cruz, and Gila rivers in southeastern Arizona, where the Sobaípuri irrigated crops and constructed settlements in rows of elongated houses.

Some of the sites had been excavated before, in the 1950s and ’60s, revealing evidence of the Sobaípuri’s signature oblong building style and plainware pottery. But, using ethnographic accounts, historical records, and the dating technology available at the time, most experts estimated that the Sobaípuri lived in Arizona no earlier than the 1540s, around the time that the Spanish arrived.

For her research, however, Seymour turned to new methods. One of them, called thermoluminescence, can pinpoint the last time a material was heated to a certain temperature; another, optically stimulated luminescence, can isolate when particles like quartz or feldspar were last exposed to light.

Together these technologies can help date objects like cooking pits, identify when pottery was fired, and determine how long some sediments have been buried.

Using this suite of techniques and radiocarbon dating, Seymour said, the more samples she looked at, the more “unusual and unexpected” the results became.